High affinity and stereospecific receptors for benzodiazepines have been identified in the mammalian central nervous system. It is currently believed that the interaction of benzodiazepines with their receptors initiates a series of neuronal events resulting in an enhancement of GABA-mediated chloride permeability. The latter results behaviorally in the major pharmacological actions of benzodiazepines, namely their anxiolytic, anticonvulsant, hypnotic, and muscle relaxant actions. In addition to benzodiazepines, a variety of sedative/hypnotic agents of the minor tranquilizer class appears to interact with one or more components of the benzodiazepine/GABA receptor complex, and thus the latter has been proposed as a common site of minor tranquilizer action. Several aspects of the benzodiazepine/GABA receptor complex are currently being studied, including purification of the receptor by affinity chromatography, characterization of multiple binding sites on the receptor complex with recognizes agonists, antagonists or inverse agonists, strain and genetic differences in receptor and number and conformation, the behavioral and biochemical effects of novel (non-benzodiazepine) anxiolytics as well as "anxiogenic" inverse agonists, and the identific- ation of a novel benzodiazepine receptor in the CNS for 4-chlorodiazepam (Ro5-4864, the so-called peripheral benzodiazepine receptor ligand.